Nutritional Value of Insects and Ways to Manipulate Their Composition
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Wageningen Academic Journal of Insects as Food and Feed, 2020;2020 online##(##): 1-21 ARTICLE IN PRESS Publishers SPECIAL ISSUE: Advancement of insects as food and feed in a circular economy Nutritional value of insects and ways to manipulate their composition D.G.A.B. Oonincx1* and M.D. Finke2 Animal Nutrition Group, Wageningen University and Research Centre, De Elst 1, 6708 WD Wageningen, the Netherlands; Mark Finke LLC, 17028 E Wildcat Dr., Rio Verde, AZ 85263, USA; [email protected] Received: 5 June 2020 / Accepted: 3 September 2020 © 2020 Wageningen Academic Publishers OPEN ACCESS REVIEW ARTICLE Abstract This article reports on the nutrients present in insects and factors affecting their variability. Data on protein content and amino acid profiles of a variety of insect species are discussed and their amino acid profiles compared to nutrient requirements of growing broiler chicks, catfish, trout, swine, and human adults and young children. Both in vitro and in vivo protein digestibility data for a variety of insect species is presented and factors affecting these data are discussed. Furthermore, the fat content and fatty acid profiles of a variety of insect species is reviewed, with special attention on omega-6 and omega-3 fatty acids. Information on carbohydrates, fibre and chitin in insects is shown along with potential effects on nutrient availability. This is followed by a discussion of essential minerals in insects with an emphasis on calcium and phosphorus. Data on insect vitamin content is shown along with a discussion of antinutritional factors such as phytate and thiaminase, which can adversely affect their nutritional value. Dietary effects on insect nutrient composition are reviewed with an emphasis on essential minerals, heavy metals, vitamin E, and carotenoids. Lastly, the effects of processing, including protein extraction and various cooking methods on insect composition are discussed. In summary, this article provides an overview of the nutrient content of insects, and how select nutrients can be altered. Keywords: amino acids, fatty acids, vitamins, minerals, digestibility, nutrient manipulation 1. Introduction article will summarise this compositional data, focus on nutrients that have received little attention and nutrient Insects are important sources of nutrients for humans and manipulation. Data on both wild and produced insects is a wide variety of other animal species. Hence studies on discussed. insect nutrient composition can be found in disciplines ranging from anthropology to zoology. Comprehensive 2. Nutrient content of insects literature reviews of insect nutrient content have been published (Bukkens, 1997; Finke, 2004; Payne et al., 2016; Protein and amino acids Raubenheimer and Rothman, 2013; Rumpold and Schluter, 2013a). While the first mention of using insects to feed The protein content of insects varies between 25 and 75% on production animals was in 1919 (Linder, 1919), it was not a dry matter (DM) basis (Barker et al., 1998; Bukkens, 1997; until the 1960s and 1970s that research started in earnest Cerda et al., 2001; Finke, 2002, 2013, 2015a; Oonincx and (Calvert et al., 1969; Hale, 1973; Teotia and Miller, 1973, Dierenfeld, 2012; Oonincx and Van der Poel, 2011). Proteins 1974; Ueckert et al., 1972). The renewed interest in this are composed of amino acids and the true protein content area of study in the last decade yields numerous papers equals the sum of amino acids. However, protein content is and comprehensive reviews regarding the safety of insects generally estimated by multiplying nitrogen content with as food and feed, as well as several overviews of feeding a protein factor (Kp) of 6.25. This results in the so-called https://www.wageningenacademic.com/doi/pdf/10.3920/JIFF2020.0050 - Monday, March 29, 2021 6:07:30 AM Wageningen University and Research Library IP Address:137.224.11.139 trials for production animals (Gasco et al., 2019; Henry et crude protein content. This factor is underestimated if not al., 2015; Makkar et al., 2014; Riddick, 2014; Rumpold and all amino acids are quantified, or due to methodological Schluter, 2013b; Sanchez-Muros et al., 2014, 2016). Given issues (Oonincx et al., 2019b), such as losses of amino acids the comprehensive nature of these recent reviews, this during hydrolysis. Conversely, the presence of nonprotein ISSN 2352-4588 online, DOI 10.3920/JIFF2020.0050 1 D.G.A.B. Oonincx and M.D. Finke nitrogen from compounds, such as chitin, uric acid, and suitability also depends on the amino acid requirements β-alanine leads to overestimations of true protein content of the consuming animal. The amino acid with the lowest when using this factor (Janssen et al., 2017). An alternative concentration relative to the requirement of the animal is Kp of 4.76 for insects has been suggested based on amino called the first limiting amino acid. Table 2 shows the amino acid data on larvae of yellow mealworms (Tenebrio molitor), acid pattern of four commonly raised insect species and lesser mealworms (Alphitobius diaperinus) and black soldier compares them to the amino acid requirements of broiler flies (Hermetia illucens) (Janssen et al., 2017). Recalculating chicks, catfish, trout, swine, and adult humans and young the data from 20 insect samples including 13 species and children (NRC, 1994, 2011, 2012; WHO/FAO/UNU, 2007). different developmental stages, results in an average Kp of Methionine and cystine are usually the first limiting amino 5.81; range 4.56 to 6.45 (Finke, 2002, 2007, 2013, 2015a,b). acids in most insect species when fed to production animals This data confirms that a Kp of 6.25 is often a slight or humans. The exception appears to be house crickets overestimate. However, until data for more species and at for catfish and swine, where threonine and/or tryptophan different life stages are accumulated, retaining a Kp of 6.25 are first limiting. These calculations are supported by data can be beneficial to facilitate comparisons between studies. from animal feeding trials. Methionine and arginine are the first limiting amino acids for broiler chicks when fed The amino acids that make up true protein, are generally Mormon cricket meal (Anabrus simplex) as the sole source grouped as either nutritionally indispensable (essential) of dietary protein in purified diets (Finke et al., 1985), or amino acids or nutritionally dispensable (non-essential) when house cricket meal is the source of protein in a corn amino acids. While all amino acids are required, based diet (Nakagaki et al., 1987). Similarly, methionine is nutritionally indispensable amino acids cannot be the first limiting amino acid in a corn-soy-meat meal diet synthesised by most animal species and must be provided for growing chickens when dried maggot meal substitutes in the diet. Variation in amino acid patterns between life for meat meal (Bamgbose, 1999). Methionine is also the stages of a species partially depends on whether that species first limiting amino acid when adult Mormon cricket meal undergoes complete metamorphosis (holometabolous) (Finke et al., 1987), yellow mealworm larvae meal (Goulet or incomplete metamorphosis (hemimetabolous) (Finke, et al., 1978), or house fly larvae meal are fed to growing 2002; Pieterse and Pretorius, 2014). Comparison of the rats (Onifade et al., 2001). The high amino acid scores of amino acid pattern (mg amino acid/g crude protein) for all four insect species for both children and adults suggests the hemimetabolous house cricket (Acheta domesticus) they are a high-quality protein source for humans. suggests that amino acid composition is fairly constant and unaffected by diet or life stage (Table 1). Similarly, Protein quality is also determined by digestibility and black soldier fly prepupae raised on eight different diets hence amino acid availability. Amino acids from insect had similar amino acid patterns (Spranghers et al., 2017; meals are readily available when fed to poultry with values Wang et al., 2020), as did tobacco hornworm larvae equal to, or higher than, those from conventional protein (Manduca sexta) fed two different diets (Landry et al., sources, such as soybean meal or fish meal (Table 3). The 1986). This suggests that for holometabolous species only exception is black solder fly larvae meal which has amino acid patterns are fixed within a specific life stage. lower amino acid digestibilities especially for the sulphur Body parts, such as wings, legs or mandibles, have specific containing amino acids, methionine and cystine (DeMarco physical requirements to function properly; therefore, it is et al., 2015; Schiavone et al., 2017). Larvae (Liland et al., unlikely that their amino acid composition can be altered 2017; Schmitt et al., 2019; Tschirner et al., 2015) and by diet. Amino acid patterns between different life stages prepupae (Spranghers et al., 2017; Wang et al., 2020) of of holometabolous insects would however be expected this species have a highly variable mineral content, which to differ because larvae and adults are morphologically is influenced by their diet. As some protein is bound to dissimilar. This was confirmed for yellow mealworms, their mineralised exoskeleton, an increased mineral content where the amino acid pattern for larvae differed from the might decrease their digestibility. Therefore, amino acid harder bodied adults (Finke, 2002). The adults contain more and protein digestibility in poultry might be increased by glycine (52%) and tryptophan (37%) than mealworm larvae, raising this species